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From: Neon John on 11 May 2010 12:18
Time to come out of long time lurk mode.

I'm doing my first foray into 0.5mm pitch surface mount with a 100 pin
TQFP FPGA. My antique eyes and 7 power surgical stereoscope (head
mounted) are not cutting the mustard. Therefore I'm looking for some
recommendations on a good stereoscope for EE work.

John Larkin, I think that it was you who posted a photo of your
workstation and a description of the scope that you use but I can't
seem to find it in the archives. Could you please re-post that info?

If anyone has a scope for sale, please contact me at
jgd(at)neon-john.com.

I would also welcome tips on how to approach this soldering problem. I
have a hot air rework station and a fine pitch soldering iron but,
mainly because of my lack of vision, I'm not doing too well.
Specifically, I can't keep the chip centered on the pads on all 4
corners. The solder doesn't suck the chip in line like larger SMD
parts do.

Thanks,
John
http://www.neon-john.com
From: D Yuniskis on 11 May 2010 12:35
Hi John,

Neon John wrote:
> Time to come out of long time lurk mode.
>
> I'm doing my first foray into 0.5mm pitch surface mount with a 100 pin
> TQFP FPGA. My antique eyes and 7 power surgical stereoscope (head
> mounted) are not cutting the mustard. Therefore I'm looking for some
> recommendations on a good stereoscope for EE work.

I use an old B&L stereoscope that gives me 7X to 30X.
It is mounted on a very *sturdy* (2" dia), 24" long arm
affixed to a hefty, cast iron base (i.e., it stays where
you put it). So, I can freely access almost any part of
a ~20+ inch panel without having to rotate the panel, etc.

I have a CCD camera that couples to one of the eyepieces
for those times when I don't want to stay hunched over the
'scope for extended periods. You lose the stereo vision
but it is often easier/more comfortable to go this route
when doing an overall inspection of a board (i.e., looking for
spots to examine more closely).

[it's also handy for capturing pictures of bad manufacturing
issues]

> John Larkin, I think that it was you who posted a photo of your
> workstation and a description of the scope that you use but I can't
> seem to find it in the archives. Could you please re-post that info?
>
> If anyone has a scope for sale, please contact me at
> jgd(at)neon-john.com.

I can probably find another "head" -- but sans base. I'll
have to look around. It might have found its way to the
metal recycle bin...

> I would also welcome tips on how to approach this soldering problem. I
> have a hot air rework station and a fine pitch soldering iron but,
> mainly because of my lack of vision, I'm not doing too well.
> Specifically, I can't keep the chip centered on the pads on all 4
> corners. The solder doesn't suck the chip in line like larger SMD
> parts do.

If there are no pads *beneath* the device (e.g., BGA), there
are some "low tack" adhesives that can sometimes help.
From: Nial Stewart on 11 May 2010 12:43
> John Larkin, I think that it was you who posted a photo of your
> workstation and a description of the scope that you use but I can't
> seem to find it in the archives. Could you please re-post that info?

I think John's got a Mantis....

http://www.visioneng.com/

...which the assembly crowd I use say are about �1K ($1.5K ish?).

> I would also welcome tips on how to approach this soldering problem. I
> have a hot air rework station and a fine pitch soldering iron but,
> mainly because of my lack of vision, I'm not doing too well.
> Specifically, I can't keep the chip centered on the pads on all 4
> corners. The solder doesn't suck the chip in line like larger SMD
> parts do.

Do two opposing corner pins with a soldering iron and fine solder. Don't
worry about shorts initially as you're just using them for mechanical
positioning. Then do the other two rows and finally the rows with the
first two pins. I do these by flooding the row with flux and dragging
a solder blob down the row. This takes some practice but if I get the
angle of attack of the iron right I can do a whole row in one pass and
just have to tidy up a couple of pins at the end with solder wick.



Nial.


From: Rich Webb on 11 May 2010 12:54
On Tue, 11 May 2010 12:18:31 -0400, Neon John <no(a)never.com> wrote:

>Time to come out of long time lurk mode.
>
>I'm doing my first foray into 0.5mm pitch surface mount with a 100 pin
>TQFP FPGA. My antique eyes and 7 power surgical stereoscope (head
>mounted) are not cutting the mustard. Therefore I'm looking for some
>recommendations on a good stereoscope for EE work.

I've been pretty happy with a
<http://www.microscope.com/omano-om24l-dual-power-compact-stereo-microscope-case-p-134.html>

Not too expensive, stage lighting is LEDs from batteries in the base,
optics are reasonable, case is included.

I mostly reserve it for inspections, though, and prefer to actually work
using an Optivisor.

--
Rich Webb Norfolk, VA
From: linnix on 11 May 2010 14:36
On May 11, 9:18 am, Neon John <n...(a)never.com> wrote:
> Time to come out of long time lurk mode.
>
> I'm doing my first foray into 0.5mm pitch surface mount with a 100 pin
> TQFP FPGA.  My antique eyes and 7 power surgical stereoscope (head
> mounted) are not cutting the mustard.  Therefore I'm looking for some
> recommendations on a good stereoscope for EE work.  

My daughter is going to college, so you know I am not too young. I
have been doing 64 pads 0.5mm QFN by hands and naked eyes, until
volume is high enough by machine.

> I would also welcome tips on how to approach this soldering problem. I
> have a hot air rework station and a fine pitch soldering iron but,
> mainly because of my lack of vision, I'm not doing too well.

Use direct sunlight if possible. I can't see them indoor, but OK
outdoor.

> Specifically, I can't keep the chip centered on the pads on all 4
> corners.  The solder doesn't suck the chip in line like larger SMD
> parts do.

Reflow will adjust the position if you have it mostly correct. You
have to heat up all 4 edges at the same time. Alternatively, you can
heat it up on the bottom.

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